An engine control module of an internal combustion engine controls the mixture of fuel and air supplied to combustion chambers of the engine. After the air/fuel mixture is ignited, combustion takes place and the combustion gases exit the combustion chambers through exhaust valves. The combustion gases are directed by an exhaust manifold to a catalyst (or “catalytic converter”) and/or other exhaust aftertreatment components.
During certain engine operating conditions combustion gases may enter the exhaust system while components of the aftertreatment system, such as the catalyst, are not yet heated to operating temperatures at which they can adequately reduce or oxidize certain regulated exhaust gas constituents. The issue typically occurs following a cold engine startup. During a cold start (also referred to as “startup period”), relatively cold exhaust system components can have large thermal masses that act as heat sinks, thereby slowing down heating of the exhaust system and the catalysts contained therein to an operating temperature at which the components adequately reduce or oxidize the regulated constituents. Therefore, during the startup period, a slow temperature rise in exhaust system components can lead to undesirable emission levels, due to the corresponding slow response and light-off (i.e. activation) of the exhaust system catalyst(s).
In addition, during the startup period certain moving components of the engine may operate inefficiently due to the fact that the components are relatively cool. After the startup period, these components are heated sufficiently to provide improved efficiency.